Which action is most likely to stop succession and make an ecosystem less stable?
O A. Using fewer pesticides in gardens
B. Using less fertilizer in gardens
C. Planting a variety of native species in gardens
D. Planting nonnative species in gardens

The answer is D.  Because planting nonnative species is bad for the area because the plants that normally grow there have to compete with that new species then.  

D. Planting nonnative species in gardens.

Explanation:

Planting nonnative species in gardens are bad for your garden. The nonnatives can steal most to all of your native plants food and they can attack your native plants and kill them.

Drug abuse and addiction have been inextricably linked with HIV/AIDS since the beginning of the epidemic. While intravenous drug use is well known in this regard, less recognized is the role that drug abuse plays more generally in the spread of HIV by increasing the likelihood of high-risk sex with infected partners.3 The intoxicating effects of many drugs can alter judgment and inhibition and lead people to engage in impulsive and unsafe behaviors. Also, people who are abusing or addicted to drugs may engage in sexually risky behaviors to obtain drugs or money for drugs. Nearly one-quarter of AIDS cases stem from intravenous drug use, and one in four people living with HIV/AIDS in the period of 2005–2009 reported use of alcohol or drugs to an extent that required treatment.